Butterfly valves have been available to industry for some time. They typically have a long service life and are light weight, inexpensive, and known for their reliability. Butterfly valves include a body having inlet and outlet ports and, a resilient or flexible seal, and a disc or mounted for rotation with a shaft, so that the disc is rotated to close off flow through the seat area, open flow through the seat area, or throttle flow through the seat area. Butterfly valves handle a wide variety of liquids, gases, and solids, including water, air, petroleum, paint, and chemicals. They are used extensively in hot-process applications; water treatment; HVAC; mining operations; paper milling; flow control of dry pellets, beads, chemicals, and feed stocks; and vacuum applications. They are available in lugged, wafer, and flanged body styles.
On center disc/seat valves are the most common type manufactured worldwide. As compared to off-center disc/seat valves, on center disc/seat valves usually have higher flow capacity, but lower pressure ratings and a shorter cycle life.
As compared to on-center disc/seat valves, off-center disc/seat valves have higher inherent pressure ratings, higher resistance to fluid transients (hammer), and higher integrity, longer cycle life seats. Off-center seating is less commonly used in resilient (elastomeric) seated industrial valves. The seating may not be fully rated bi-directional. Additionally, the operating torque is typically higher in one direction versus the other. This impacts the cost of the valve because the size of the actuator must be increased to overcome the operating torque during opening and closing of the off-center valve in the high operating torque direction.
On-center and off-center disc/seat butterfly valves and serve their respective objectives and, therefore, both types are in demand. Unfortunately, this requires manufacturers, distributors, and at times valve users to maintain a costly inventory of both valve types.
Accordingly, a butterfly valve with interchangeable on-center and off-center discs that use a common body will substantially reduce inventory and allow easy retrofitting of butterfly valves with alternate interchangeable on-center and off-center discs.